Preparation And Study Of Hydrogels With Complex Shape Deformations And Special Hollow-formed Structure Induced By Ions

During the preparation of hydrogels,most of the researchers have focused on the regulation of the composition of hydrogels to change the performance of hydrogels,while ignoring the effect of the structural design and the controlment of preparation process on the performance of final hydrogels.In this paper,we mainly used the ion-induced method,combined with reasonable structural design and controlled preparation process to expand the functional applications of the hydrogels.Firstly,tough hydrogels with complex shape deformations have been prepared through the reasonable structural design.And then,the external morphology and internal structure of the high-strength hydrogels were controlled by reasonable regulation of the preparation process.Under certain external stimuli,the changes of the crosslinking density and volume of the intelligent responsive hydrogel can induce the deformation responsiveness of the hydrogel.In this paper,we prepared an ion-induced responsive hydrogel actuator based on the ionic coordination interaction between the carboxyl and Fe³⁺.Firstly,the D-CMC-Fe³⁺/PAAm high strength hydrogels with highly adjustable mechanical properties were prepared by using three different DS of sodium carboxymethyl cellulose?CMC??DS = 0.7,0.9 and 1.2?.The maximum tensile strength of this hydrogel can be up to 1.6MPa,the correspo nding elongation at break is 700%.Then by selectively introducing the p?AAm-co-AAc?hydrogel strips into the CMC/PAAm bulk hydrogel,the CMC/PAAmllp?AAm-co-AAc?hydrogel with inhomogeneous distribution of the carboxyl content was obtained.The differences of the carboxyl content between the selective implanted sites and bulk parts of the hydrogels caused the heterogeneous shrinkage after immersing the hydrogel into Fe³⁺ solution,which drove the large angle folding deformation,the folding angle can vary from 0° to 180°.By altering the shapes,sizes and locations of the selectively implanted p?AAm-co-AAc?hydrogels,the ion-induced responsive hydrogels with controllable folding angle and complicated shape deformations could be easily achieved.The simple “V”,“U”,“Z”,“S”-shaped,and even the petal and cube hydrogels can be easily prepared in Fe³⁺ solution.We believed the superior mechanical and shape-programmable property can endow the hydrogel actuator with potential application prospect in underwater switch and underwater manipulator.Good mechanical properties,designable external morphology and simple preparation process is extremely important for the practical application of hydrogels.Here three natural components of gelatin,chitosan and sodium citrate were applied to prepare high strength,biocompatible hydrogels with controllable designability of the external morphology and internal hollow structure.The compressive strength of the multiple physically crosslinked hydrogels can be up to 5.52 MPa.Different from the traditional ways to prepare complex-shaped hydrogels,the novel thermal welding and etching approaches were used here to program the external morphology and construct complicated shapes,which avoided the usage of the complicated and expe nsive mold.Besides the ideal designability of the external morphology,the hydrogels exhibited a special hollow-formed character.By applying an interrupted ion crosslinking process in controlled immersing time in sodium citrate solution and the subsequently dissolving process at physiological temperature in deionized water.The special hollow "cup-shaped and tubular" structure with controllable hollow size can also be formed.The special hollow-formed character was attributed to the synergy of two mechanisms: the time dependency of the ionic diffusion,and the thermally reversible gelation of gelatin hydrogel.The high strength,biocompatible hydrogels with special internal and external shape adjustable characters,potentially useful in vascular repair and substitutes of cartilage,may further broaden our understanding of the plasticity of the hydrogels.